Ring Main Extension

[Bon]

Hi all,

I'm planning on adding a couple of sockets into my spare room (one at low level & one at mid-wall level for a TV/monitor). I have a socket on the opposite wall of the same room and another socket in the next room on the wall that backs onto that. Rather than messing about with junction boxes; my plan is to replace the interconnecting cable between to the two existing sockets and extend the ring. I know I can't spur off the ring as I want to add 2 sockets.

I'm still in the "doing the job in my mind" phase by the way!

So, my question is - how do I identify which is the interconnecting cable without hacking out the wall and floor on both sides of the wall? Any hacking would preferably be kept to a minimum as I will have to get the ply sheets up to run the new cable to the new socket location (new house so no nice narrow boards to lift!).

Any help would be much appreciated.

 

[PrenticeBoyofDerry]

If the ring final, is a true ring with no spurs or branches, then it should not make much difference which leg you use, but to answer your question, you would need a continuity test meter to test end to end of the conductors. You will also require 30mA RCD protection on the circuit, to comply to regs for newly installed sockets

 

[ban-all-sheds]

Rather than messing about with junction boxes; my plan is to replace the interconnecting cable between to the two existing sockets and extend the ring.

1) How do you know that there is a cable between those two sockets?

2) The one in the room where you want the new sockets is one the opposite wall - what route would the cables take to get to and from the new sockets?

I know I can't spur off the ring as I want to add 2 sockets.

You could have a fused spur.

So, my question is - how do I identify which is the interconnecting cable without hacking out the wall and floor on both sides of the wall?

By a combination of looking to identify the likely suspect(s) and continuity testing with your multimeter. You would have to test at every likely socket in the vicinity to make sure you'd found a single cable.

Really, positive visual identification is the best way.

Any hacking would preferably be kept to a minimum as I will have to get the ply sheets up to run the new cable to the new socket location (new house so no nice narrow boards to lift!).

If you take up the floor you might be able to see the cables just fine.

Are you sure it's a suspended floor?

Are you sure you can route cables underneath it?

Do the joists, if any, run in a helpful direction?

www.bing.com/images/search?q=solid+board+cutter

 

[ban-all-sheds]

If the ring final, is a true ring with no spurs or branches, then it should not make much difference which leg you use,

It does if he disconnects what he thinks runs from one socket to the next and doesn't join his new cable to the old.

 

[Bon]

Thanks for the quick reply!

The house is a 2011 build and looks as if the CU has RCDs in it (there are 2 30mA RCDs labelled "RCD protected circuits"). Would these protect individual circuits (like garage supply for example) or do they protect all circuits?

Thanks again

 

[Bon]

1) How do you know that there is a cable between those two sockets?

2) The one in the room where you want the new sockets is one the opposite wall - what route would the cables take to get to and from the new sockets?

1 - I don't. Just "seems" logical although as a Mechanical Engineer - I often find what I find logical to be at odds with by Electrical "cousins!"

2 - If the joists run wall to wall then I'll get the cable into the channel that leads to the location of the new socket. If not I'll have to drill/notch the joists

You could have a fused spur.

I'm listening!

Really, positive visual identification is the best way.

Thought you might say that

If you take up the floor you might be able to see the cables just fine.

Fingers crossed!

Are you sure it's a suspended floor?

Are you sure you can route cables underneath it?

Yes and yes

Do the joists, if any, run in a helpful direction?

Probably not. Will know more when the floor's up I suppose!

Thanks by the way.

 

[PrenticeBoyofDerry]

Thanks for the quick reply!

The house is a 2011 build and looks as if the CU has RCDs in it (there are 2 30mA RCDs labelled "RCD protected circuits"). Would these protect individual circuits (like garage supply for example) or do they protect all circuits?

Thanks again

It would depend on how your board is configured but normally you would expect to find on dual RCD board, that the two RCDs are split across the circuits of the property. So possibly each RCD is protecting say 5 circuits each if you have 10 circuits in the property, but it could be totally different.

With regards to spurring of RFC, you could take a double socket off any socket that has not already been spurred from, or you could fit a 13A FCU at the feed socket then spur multiple sockets from that, but you will be restricted to 13A load on the additional sockets.

 

[PrenticeBoyofDerry]

If the ring final, is a true ring with no spurs or branches, then it should not make much difference which leg you use,

It does if he disconnects what he thinks runs from one socket to the next and doesn't join his new cable to the old.

That's why they need to test out for continuity, providing they can prove that is correct, then they can intersect the new sockets in either leg.

 

[ban-all-sheds]

 

[Bon]

Yes, that was my original question. I think it was answered by your good self a few posts up in that having a look is the best bet.

Many thanks.

 

[ericmark]

OK with mains isolated and some where on the ring a load is plugged in say a kettle then both sockets off and wires disconnected then to CU unit will have a reading of some ohms line to neutral and to other socket would show open circuit.

However what you don't know are there any other sockets on the wire being disconnected?

So one would need to test for that load on every socket and FCU to ensure there is nothing feed from that interconnecting wire.

OK it can be done but unless the load on the new sockets is going to be very high then swap a selected socket back box for a twin back box

and fit a fused connection unit (FCU) alongside the original sockets and then you can have as many sockets as you like from the FCU with out any worries about getting right wires or right pair of sockets and also no problem with loop impedance or volt drop readings.

 

[ban-all-sheds]

Well if he replaces one existing socket with two singles in a dual box, puts one existing cable into one of them, the other into the other, then he can run a loop of new cable to the new sockets and know he's extended the ring.

 

[winston1]

[quote


If not I'll have to drill/notch the joists

[/quote]

I'm listening!

Good. Notching joists is not allowed. Too easy to put a nail through a cable when replacing floor. Joists should be drilled at approx half their depth.

 

[DaftPunk]

Notching joists IS allowed. The iet even recommends reusing notches where they are already present. Wrong again winny boy

 

[winston1]

Notching joists IS allowed. The iet even recommends reusing notches where they are already present. Wrong again winny boy

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